Modern aircraft typically have a number (e.g., four) of air data sensor probes (“ADSPs”) usually mounted in the nose portion or aft of the nose portion of the aircraft (e.g. two probes symmetrically located on each side of the tip of the nose portion or aft of the nose portion). These sensor probes sense various characteristics of the airflow passing by the aircraft, including various pressures (e.g., static and dynamic) and temperatures.
Also, modern aircraft commonly use an ADSP that includes a computer or data processor contained within the body or housing of the ADSP. As such, these “self-contained” ADSPs are connected in a “distributed” manner within the aircraft as part of an overall air data system. The ADSPs or the air data system send processed signals indicative of various aircraft characteristics to the flight control computer and/or avionics module on the aircraft for further processing and use for control of the operation of the aircraft. These processed signals may include, among others, the angle of attack and the angle of sideslip of the aircraft in flight, along with aircraft altitude, true and calibrated airspeed, and Mach number. These processed signals are generated by each ADSP from the pressures and temperatures sensed by the ADSPs and are critical to aircraft performance.
Advantages of the self-contained ADSPs include the elimination of the pneumatic tubing required for the older style sensors that did not contain a computer or processor. Other advantages include reduced weight and power consumption, higher reliability, elimination of separate angle of attack transmitters, elimination of separate probe heater current monitors, elimination of skin effects on static measurements, and elimination of pressure lag and pressure checks on the flight line.
However, these self-contained ADSPs are not without their drawbacks. Similar to the older style sensors that did not contain a computer or processor, such newer self-contained ADSPs are also vulnerable or prone to blockage of the pressure ports on the probes by various types of environmental contaminants, such as, for example, icing, ash, insects, liquid ingress, foreign object damage, etc. By its nature, the source of the contamination may affect many, if not all, of the ADSPs. This common cause effect can defeat prior art monitoring strategies relying on comparison of similar signals generated by different air data probes or sensors. It is especially difficult to identify probes with blocked ports when a majority of the ADSPs are contaminated. An air data system with relatively many contaminated ADSPs may generate undetected erroneous data, resulting in potentially catastrophic consequences for the aircraft. For example, the effect of erroneous air data on the aircraft—and on the flight control system in particular—received much attention following the crash of Air France Flight 447. Essentially, it has been shown that modern aircraft are relatively very sensitive to certain types of errors in the air data system.
Known, prior art air data probe contamination monitoring solutions relying on probe to probe comparisons are unable to detect, in every aircraft flight phase, when a majority (or even more than one) of the ADSPs are contaminated. This is particularly true for the modern, fly-by-wire (“FBW”) type of aircraft flight control system. Such FBW systems generally include comparison monitoring of air data probe signals to detect and reject a single ADSP failure, and they may also provide for resolution of a generic hardware failure with the air data system. However, a typical FBW system cannot detect the existence of matching erroneous outputs from three or four ADSPs.
It is known to utilize model-based approaches (e.g., in-line reasonableness monitoring) for air data probe contamination monitoring in FBW or other, more classical types of aircraft flight control systems. However, these approaches are relatively complex, are processing intensive, and are unable to cover for every aircraft flight phase.
A FBW flight control system commonly comprises a computer system interposed between: (1) the flight control inputs given both automatically by various aircraft component sensors and subsystems (e.g., the air data system) and manually by the pilots via, e.g., sidestick or yoke controllers, switches, levers, etc.; and (2) the aircraft flight control surfaces and other devices that ultimately control the operation and direction of the aircraft in flight. That is, the inputs from the pilots and the sensors are not connected directly to the aircraft flight control surfaces to be controlled (e.g., ailerons, rudder, elevators, spoilers, slats, flaps, etc.). Instead, the pilot and sensor inputs are routed to a computer system (e.g., typically comprising more than one computer or data processor device for safety redundancy purposes) that contains the flight control logic which interprets the sensor and pilot inputs and outputs flight control surface position commands that move the aircraft flight control surfaces according to control laws (“CLAWS”) stored in the computer system to effect changes in the aircraft's pitch, roll, yaw, altitude, etc., for example.
What is needed is an improved aircraft flight control system having an air data probe contamination monitor which senses any contamination with the one or more air data sensor probes located on the aircraft and provides an indication thereof to the aircraft flight control system or avionics module so that corrective action can be taken to avoid a potentially dangerous condition for the aircraft.